Antenna on Predator Drone (predatorDrone.sdf)

Problem Description

This problem illustrates how to obtain the far field radiation patterns of a current source antenna mounted on a Predator Drone.

This simulation can be performed with a VSimEM license.

Opening the Simulation

The Predator Drone example is accessed from within VSimComposer by the following actions:

• Select the New → From Example… menu item in the File menu.
• In the resulting Examples window expand the VSim for Electromagnetics option.
• Expand the Antennas option.
• Select “Antenna on Predator Drone” and press the Choose button.
• In the resulting dialog, create a New Folder if desired, and press the Save button to create a copy of this example.

The Setup Window is now shown with the CAD imported geometry and antenna current distribution accessible to the user. See Fig. 209.

Fig. 209 Setup Window for the Predator Drone example.

One can click and unclick the grid, the farFieldBox0 in the histories, the current distribution, and so forth to see where those objects are. One can change locations through changing the values under Constants or, in some cases, the numbers directly in the objects.

Simulation Properties

This file allows the modification of antenna operating frequency, source amplitude, dimensions of the source and the Kirchhoff box by changing the associated variable values under the Constants.

Running the Simulation

After performing the above actions, continue as follows:

• Proceed to the Run Window by pressing the Run button in the left column of buttons.
• To run the file, click on the Run button in the upper left corner of the Logs and Output Files pane. You will see the output of the run in the right pane.
• The run has completed when you see the output, “Engine completed successfully.” This is shown in Fig. 210.

Fig. 210 The Run Window at the end of execution.

Analyzing the Results

After the run, one must analyze the Kirchhoff box data to get the far fields. This is done as follows:

• Proceed to the Analysis window by pressing the Analyze button in the left column of buttons.
• Click on the Show All Analyzers button, then click computeFarFieldFromKirchhoffBox.py, then click on the Open button as shown in Fig. 211.

Fig. 211 Choosing the Kirchhoff Box Analyzer.

If you want, you can grab the dividing bar between the list of Analyzers in the Analysis Controls window and the Analysis Results window, and slide it left to cover up the Analysis Controls window, making more room for the Analysis Results window.

The default values should all be good, but one must set farFieldRadius. Since the box size is one, it is sufficient to choose 10.

The analysis script will compute the instantaneous far fields at the timeStepStride. You may also optionally compute the Fourier amplitude at a single frequency. As this is a single frequency excitation, at 1 GHz, the Fourier amplitude is indeed of interest, and so you should also set getFourierComponent to 1, and set frequency to 1.0e9.

If you want the script to run faster, lower numTheta to 8 and numPhi to 16.

• You will also usually want to choose Overwrite Existing Files.
• Hit the Analyze button in the top left of the window.

At completion, you will see Fig. 212. The far field data is written to vsh5 files in the simulation directory.

Fig. 212 The Analysis window at the end of execution.

Visualizing the Results

Proceed to the Visualize Window by pressing the Visualize button in the left column of buttons.

The radiation pattern in real space can be visualized by doing the following:

• Expand Scalar Data
• Expand E
• Select one of the scalar fields, such as E_x
• Move the Dump slider to see the far field pattern at different times.

It is useful to reset the color minimum and maximum using the Colors button and the number of Contours, to give a pleasing pattern, as shown in Fig. 213. An odd number of contours will result in a contour at zero field, which often leads to a less attractive plot with the zero contour filling up the space. Thus, in this case, an even number of contours is suggested.

Fig. 213 The radiation pattern in real space

The far field radiation pattern, which was computed in the section on Analyzing the Results can also be displayed. Remove the previous image. Then check the PdBi box under Scalar Data, and move the dump slider to the beginning dump. You will see a 3D radiation surface, representing the Far Field radiation power level at each angle that was processed. Colors and radius are in units of dBi, decibels relative to isotropic. A notable peak in the radiation pattern is evident in the forward, upward, and downward directions, as seen in Fig. 214.

Fig. 214 The far field radiation pattern

Further Experiments

Upon close inspection you will note that the mesh size is slightly too large to fully resolve the thin wing structures of the tail section. You can experiment with smaller cell size to resolve these structures. Beware that more cells will increase the run time.

This example can be extended to meet any antenna placement problem with by addition of parameters to define the current distribution center. The vertical extent of the simulation box could be shrunk to reduce the simulation time, which would then allow greater resolution of the wavelength.

The main driver of simulation accuracy is the number of points per wavelength. Because of this lower frequencies will simulate in less time as they require fewer cells to achieve the same resolution in the wave.